1. Field of the Invention
This invention relates to telescoping masts for antennas on mobile electronics platforms, such as television and communications support trucks.
2. Description of Prior Art
Vertical retractable masts are often provided on mobile communications support vehicles for television news reporting support. The mast is composed of a series of nested tubes. The mast is extended by pumping compressed air into the largest tube at the bottom. Each tube acts as a piston within the next larger tube. The mast remains extended by retaining an air pressure differential with respect to ambient air pressure. Supplemental periodic air pumping may be needed to compensate for leakage.
The purpose of the mast is to raise one or more antennas to a workable height above the ground and above the vehicle. Electrical cables for the antennas must extend and retract with the mast. The cables required for a given antenna installation are pulled through a cable sheath that is adapted for this use. The type of cable sheath in current use is a semi-flexible tube formed into a helix surrounding the mast. The helix extends and contracts with the mast.
Since the cables circle the mast repeatedly in the helix, the total length of the cables is more than twice the height of the mast. Longer electrical cables need larger conductors and better shielding to avoid signal loss. This combination of excess cable length and size multiplies the weight of the cables supported by the mast. In turn, this multiplies the strength and air pressure requirements for the mast, making it heavier, more expensive, and requiring a heavier vehicle to support a given payload. Conversely the heavy cables reduce the payload that can be supported by the mast and the payload that can be carried by the vehicle.
In addition to this problem, it is difficult to pull electrical cables through the helical sheath. The sheath must be stretched and held straight while the cables are pulled through it. This requires a very long workbench and mechanisms to stretch the cable to a nearly straight condition. The sheath must have substantial form-holding elasticity to return to a helical shape. Thus, the sheath itself is heavy and expensive.
Furthermore, the helix can catch the wind and swing from side to side, causing additional stress on the mast that must be accommodated in the mast strength.
The objectives of the present invention are provision of a cable reel for telescoping antenna masts that minimizes cable length and weight, minimizes cable movement in wind, simplifies combining cables in an appropriate sheath, and reduces the strength requirement of the sheath. A further objective is retrofit capability for using the reel on existing telescoping masts.
These objectives are fully achieved by means of a reel mounted at the mid-point of a telescoping mast for antennas. The reel winds a multi-celled ribbon cable that passed through the hub to feed and wind in two directions at once. The reel is mounted on the mast with a clamp that fits a range of mast sizes, and distributes the weight of the reel on the mast sufficiently to avoid distortion of the mast. The reel preferably has a cable tensioner wheel on both cable feeds to prevent the cable from slipping off the reel. A selection of cables can be pulled through the multi-celled ribbon sheath by the installer to support a given installation. The outer plate of the reel can be easily removed to remove the cable sheath from the hub for changing the selection of cables in the sheath.